A US-Russian ceasefire deal for Syria was on the brink of collapse after a week of mishaps and setbacks that exposed the fragility of the plan.

The ceasefire is premised on a series of trust-building exercises that were intended to culminate tomorrow in the launch of preparations between the United States and Russia for joint airstrikes against terrorist groups in Syria.

Instead, an errant strike yesterday by the US-led coalition against Isis (Islamic State) that mistakenly killed dozens of Syrian government soldiers has exposed the deficit of trust between the two powers.

Whether US warplanes conducted the attack is in question. The US-led coalition is made up of 67 countries, more than a dozen of which carry out airstrikes against the militants.


The Defence Department of Australia, which is among the nations contributing to the effort, acknowledged in a statement that its warplanes had participated in a strike in Deir al-Zour, the eastern Syrian city where the attack occurred, on a front line between the Syrian Army and Isis that has changed hands many times.

But the strike sent tensions soaring between Moscow and Washington, the chief sponsors of the truce, casting further into doubt the likelihood that they will be able to work together to end Syria's war.

Russia continued its verbal assaults on the United States, with a Russian Foreign Ministry statement accusing the pilots who carried out the strikes of acting "on the boundary between criminal negligence and connivance with Islamic State terrorists".

The statement stopped short of accusing the United States of deliberately ordering the strike to assist Isis, but the main spokeswoman for the Russian Foreign Ministry had earlier made the allegation in televised comments, underscoring the depth of mistrust between the two powers.

In Aleppo today, warplanes dropped barrel bombs on four residential neighbourhoods, upending the relative calm that has prevailed there for a week. Aid convoys remained stalled on the Turkish border for a sixth consecutive day.

Although violence has diminished, the United Nations has accused the Syrian Government of failing to grant permission for safe passage of aid convoys.

The US Central Command said yesterday's airstrike was "halted immediately" when US forces were informed by Russia "that it was possible the personnel and vehicles targeted were part of the Syrian military". Central Command said the intended target had been Isis forces in the area.

A US defence official said the strike "appears to be an intelligence failure".

Russia and Syria asserted that 62 were killed and about 100 others were injured.

Coalition airstrikes against Isis are coordinated through US military planning cells located in the Middle East. Target tracking is done through a variety of means, including aerial reconnaissance by surveillance drones and communications intercepts.

The defence official said that the strike destroyed roughly six vehicles and the "personnel associated with them. . . . If we did get this wrong, which it looks like we did, it's not something we intended to do," the official said.